DAB+ vs. FM xmtr

What is the difference between an FM-transmitter and a DAB+/DAB-transmitter ?

What’s in the name?

The FM (Frequency Modulation) indicates how the modulator applies the analog audio to the radio frequency carrier.

The acronym DAB does not reveal how the modulator applies the audio to the carrier. It only tells us that it is a Digital Audio Broadcasting System (DAB).


There is a vast difference in the techniques used for DAB compared to FM.

FM is an analog system, while DAB should be considered an end-to-end digital system. Developers of the DAB system have introduced some cutting-edge techniques to build “the” radio broadcasting system of the future to overcome the many artifacts of the FM system.

The DAB broadcast process introduced a new step. As we will see later, a degree results in enormous advantages for a modern radio broadcasting system.

See the simplified diagram of an FM-broadcasting system and the additional functions added to the DAB system.

The significant difference is the additional step of encoding audio into a digital bitstream before transmitting and turning the audio bits back into analog audio. Manipulation of bits at a constant data rate adds a lot of possibilities to the broadcast system, such as there are:

  • Eliminating phase distortion (distortion which gets worse with an increasing distance to the transmitter, limiting the reach of an FM station)
  • Identical high-quality audio independent of the strength of the received signal (within the limits of the error correction system)
  • Perfect SFNs operation. Single Frequency Network means all transmitters are working on the same frequency allotment, which results in efficient spectrum usage.
  • DAB similar transmits audio and data in the same way. The FM system sends analog audio and digital RDS data separately.
  • Using more bits per second makes it possible to multiplex more radio stations in the same bitstream. These stations will not affect each other as they are part of the same transmission signal. Imagine 12 radio stations in a frequency spectrum of only 1.5 MHz, in the same area, not affecting each other’s audio quality. It is impossible to put 12 radio stations in one coverage area in the 1.5MHz spectrum in the FM band without radio stations interfering with one another.

Multiple stations need an Ensemble Multiplexer (MUX), meaning we will have two essential functions in front of the DAB transmitter. The Audio Encoder and the Ensemble MUX. Together they are called the DAB Headend. Software on a PC usually handles the functions of the complete DAB Headend.